The present invention broadly relates to impact protective headgear and is more particularly concerned with size adjustable impact protective headgear comprising a relatively thick impact energy absorptive skull encasing component composed of a molded cellular polymer material.
In many human sport and industrial activities, such as in bicycle racing and touring, auto racing, jogging, horseback riding, baseball, lacrosse, hockey, demolition and construction work and the like it is important that impact protective headgear be worn. A common type of impact protective headgear for such activities comprises a relatively stiff and thick impact energy absorptive skull encasing component composed of a molded cellular polymer material, such as polystyrene, copolymers of styrene and maleic anhydride or acrylonitrile, polyethylene, polypropylene or ethylene-propylene copolymers. Often, but not always, such headgear also comprises an exterior shell composed of a tough, abrasion and impact resistant non-cellular sheet polymer material such as glass reinforced polyester, polyethylene, polypropylene, polycarbonate or acrylonitrile-butadiene-styrene copolymers. In this latter instance, of course, the skull encasing molded cellular component functions as an energy absorptive liner for the shell and the overall headgear construction may be in the nature of a helmet or cap.
The relatively stiff skull encasing energy absorbing molded cellular polymer headgear components, usually having an average thickness of at least about 1/4 inch (0.635 cm) and often having an average thickness of about 1/2 inch (1.27 cm) or greater, have been found to be possessed of several important beneficial qualities which befit them for the task. Firstly, molded cellular polymer wares are generally of relatively low density, thereby allowing production of molded cellular impact absorptive skull encasing headgear components which are comfortable to wear due to their light weight. Another important benefit attributable to molded cellular polymer headgear components resides in the generally excellent energy absorptive properties thereof. Moreover, the energy absorptive qualities of such molded skull encasing headgear components can often be tailored to ideally befit the specific impact protective task to be served, such as by suitable selection of the starting expandable polymer materials and/or molding conditions.
While substantially any conventional cellular polymer molding process may be utilized in the manufacture of such skull encasing headgear components, the specific process of current commercial preference is the so-called "expandable bead" molding process. In expandable bead molding thermoplastic polymer beads, containing one or more physical blowing agents such as a fluorocarbon, propane, butane or pentane, are charged into a slightly opened steam heated mold, the mold closed and steam (or hot air) injected into the closed mold in order to expand the beads into conformance with the mold cavity and to cause them to coalesce and weld together within the mold. The thusly molded cellular product is then cooled within the mold, usually by circulating cooling water around the mold, the mold opened and the molded ware removed therefrom. Then, the molded ware is generally heat cured, in an oven, for a period of time sufficient to relieve internal molding stresses and to thereby allow the ware to assume its finished shape. By judicious control of the mold conditions and the feed material expandable polymer beads it is possible to provide the finished molded ware with a protective continuous external polymer skin as well as to control density, cell size, cell size distribution and cell wall thickness. In a variant of this general process, the expandable beads, prior to molding thereof, are first subjected to one or more stages of preexpansion by heating thereof in steam or hot air in an unconfined volume so as to avoid premature adherence of the beads to one another. Further details concerning the general methodology of expandable bead molding of polystyrene and its copolymers may be had by reference to such published works as Encyclopedia of Polymer Science and Technology, H. Mark et al, Eds., John Wiley & Sons, Inc., 1989, Vol. 16, pgs. 201-204 and Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., W. Gerhartz et al., Eds., VCH Verlagsgesellschaft mbH, 1988, Volume All, pgs. 445-447.
One of the problems associated with the relatively thick and stiff cellular polymer skull encasing headgear components of the prior art resides in the requirement for utilizing a separate and distinct mold for each of the many sizes of the component required to provide proper fitting of the finished headgear to the range of head sizes found in the human population. This, of course, adds substantially to the overall cost of manufacture. Moreover, maintaining and controlling inventories of the variously sized molded cellular polymer headgear components imposes yet another substantial burden, not only upon the protective headgear manufacturer but also upon the distributor and retailer of such goods. Accordingly, it is a highly desirable goal to provide an impact protective headgear construction comprising a molded impact absorptive cellular polymer skull encasing component whose size is adjustable over a range of head sizes. In accordance with the present invention, this goal has been achieved.